Device for producing counter pressure in pressing tools



V 1,614,404 Janr 1 1, 1927. H SKOV v DEVICE FOR PRODUCING COUNTER PRESSURE IMPRESSING TOOLS Filed March 6, 1924 Zhrnfof fiiS/ra/ y I /%lZ Patented Jan. 11 1921.

UNITED STATES PAT ENT OFF-l HENRY SKOV, OF COPENHAGEN, DENMARK, ASSIGNOR TO DANSK PRESSEFARRIK A/S, OF COPENHAGEN, DENMARK.

DEVICE FOR PRODUCING COUNTER PRESSURE IN PRESSING TOOLS.

Application filed March 6, 1924, Serial No. 697,330, and in Denmark March 8, 1923.

This invention relates to a method with appurtenant devices for producing a counter-pressure in pressing-tools used c. g. for pressing up pressed sheet metal boxes or the like matters.

The invention has for its object to secure the firm holding of the edge of the sheet metal disc, from which e. g. a box is pressed up by drawing, in such a way during the drawing that the edge of the sheet metal .disc is prevented from forming ridges. This is obtained thereby that during the pressing up the edge of the disc is held under pressure between the descending press plunger and a holding device shaped in accordance with the sheet metal disc and pressed from below against the press plunger. I The invention is mainly characterized thereby that the holding device is indirectly influenced by the air pressure of an air chamber, which pressure acts according to the invention through a liquid column filling the interior of the cylinder and pressing device transferring the pressure of the air chamber to the holding device.

The drawing represents all parts necessary to the understanding of the invention.

Fig. 1 shows schematically the device employed in an eccentric press.

Fig. 2 is a sectional elevation at a greater scale through a constructional form of the holding pressure device placed below the press table e. in the eccentric press shown in Fig. 1.

21 designates the frame base carrying the proper eccentric press 22 which is bolted thereto. The press consists chiefly of a machine i'rame of cast-iron the upper part of which forms the bearing of the eccentric shaft 23 rotated by the fly-wheel 24 which serves also as a pulley and during the r0- tation of which the head 25 in which the top-swage 5 of the press is mounted moves up and down in relation to the press table 1, Figs. 1 and 2. At the centre of the press table ther is a recess covered by the bottom swage 2 which consists of several parts viz, 1, an annular, oblong or otherwise shaped (according to the shape of the boX to be produced) cutting steel 3 serving to out out the disc to be pressed from a greater sheet metal piece by the topswage, and 2, a cylindrical or oblong core 4 over which the box is pressed up also by the upper swage the shape of which corresponds to that of the core 4. The circular, oblong or otherwise shaped sheet metal disc 6- is indicated in Fig. 2 where it is shown suspended in the air between the top and 7 bottom swages. In order to firmly keep the edge of the disc 6 during the pressing of the box and to prevent it from buckling a suitable holding device is inserted at a suitable place in connection with the top or bottom swage. In the constructional form represented in the drawing the said holding device consists of a holding ring 7 mounted in the bottom swage and holding the edge of the disc 6 by being pressed upwards against the lower surface of the upper swage 5. p

In the formerly known holding devices the holding, ring 7 was directly influenced by an air pressure in an air chamber 26 from which the pressure was transmitted to the holding ring through an air channel 27 and actuating the holder ring through a piston device subjected to the same air pressure. The known machine working only with air pressure has proved unsatisfactory in the practice as the working parts of the pressure device cannot be made tight enough for the great air pressure to be-used. I j According to the present invention the holder ring 7 is indirectly influenced by the air pressure in the air chamber 26 by means of a liquid column filling out most partof the pipe 27 and the entire cylinder and plunger device placed under the presstable and serving to press the holding ring7 upwards against the topeswage during the downward movement of the latter.

In the constructional form shown in the drawing the holding ring 7 is brought under the influence of the air pressure of the air chamber through a liquid column in the following manner:

The holding ring rests upon a number of bolts 8 passing through corresponding holes in the bottom swage 2 and standing upon the upper surface of a plate 9 which rests upon the cover plate 10 closing the upper end'oi a movable plunger 12 which is con nected with the plate 10. As shown in the drawing the proper plunger 12 is hollow and closes tight to a corresponding guiding tap 14 carried by a frame 13 which is fixed to the press table 1. The tap 14 is hollow and provided with a channel 17 corresponding through a rearwardly extending channel 18 with the pipe 27 which leads to the air chamber 26. The interior of the plunger 12, the channels 17, 18 and a corresponding portion of the pipe 27 is filled with a liquid e. g. oil which will be placed under a pres sure corresponding to the air pressure in the air chamber 26. In order to secure the necessary tightness between the guiding tap 1 1 and the hollow plunger 12 one or more packings, as e. g. the leather packing 15 and the packing box 16, may be provided.

When during the pressing up of the box the holding ring 7 is pressed downwards together with the edge of the plate 6, the ring will depress the plunger through the bolts 8 and the plates 9, 10. The descending movement of the plunger will be transferred through the liquid in the interior of the plunger and in the channels 17, 18, in connection with the pipe 27, the liquid acting owing to its lack of compressibility, as a movable plunger, the extremity of which acts upon the air in the air chamber or pressure receiver 26. The said movement of the plunger results in a diminishing ot the air space of the air chamber. This diminishe'd space leads to an increasing of pressure which is practically naught when the air chamber is great but will be noticeable when it is smaller or small. By variation of the pressure in the air chamber 26 the pressure of the holding ring may be varied according to circumstances so that it is constant during all the pressing or increased just in the proportion required,

The main feature of the present invention is that the holding device is influenced from the known air pressure device through an intermediate liquid plunger, by the insertion of which the necessary obturation is obtained so as to enable the air pressure in the air chamber to be kept constant for a long time. In order to avoid leakage of liquid special means may be employed on places where it is necessary. As a special means for tightening the leather packing 15 a resilient ring 19 is employed pressing the edge of the leather ring against the interior surface of the hollow plunger 12.

The invention is neither limited to the de vices shown in the drawing nor to its employment in combination with a holding ring, the main feature of the invention being that the correct pressure on some place of the blank 6 is produced by an air pressure influencing the blank through a liquid column so that the movable parts of the device are to be kept tight only against water pressure and not against air pressure.

I claim:

1. An air pressure cushion device for sheet metal die machines, comprising, a holding device for blanks, a closed air chamber, a plunger arranged to act on the holding device during the pressing operation, and a column of liquid for transmitting the pressure within the closed air chaml'ler to the plunger.

2. An air pressure cushion device for sheet metal die machines, comprising, a holding device for blanks, a closed air chamber, a stationary guide tap, a hollow plunger slidable on the guide tap and arranged to act on the holding device during the pressing operation, a channel leading from the closed air chamber through the guide tap and to the interior of the hollow plunger, and a column of liquid, contained in the channel, for transmitting the pressure within the closed air chamber to the plunger.

3. An air pressure cushion device for sheet metal die machines, comprising, a holding device for blanks, a closed air chamher, a stationary guide tap, a hollow plunger slidable on the guide tap and arranged to act on the holding device during the pressing operation, a channel leading from the closed air chamber through the guide tap and to the interior of the hollow plunger, and a column of liquid, contained in the channel, for transmitting the pressure within the closed air chamber to the plunger, a liquid tight connection between the end of the stationary guide tap and the sliding hollow plunger, including, an inner resilient ring, and a leather packing surrounding the ring, the ring being arranged to press the leather packing against the inner surface of the hollow plunger.

t. An air pressure cushion device for sheet metal die machines, comprising, a holding device for blanks, a hermetically sealed air chamber, a plunger in the chamber arranged to act on the holding device during the pressing operation, and a column of liquid filling the plunger chamber and in communication with the air in said air chamber.

In testimony whereof I affix my signature.

HENRY SKOV. 

